Method of lubricating metal surfaces with a vaporous lubricant



METHOD OF 'L'UBRICATING lVIETAL SURFACES WITH A VAPOROUS LUBRICANT Robert A. -Cit, Oakland, and Stanley S. Sol-em, Orinda,

Calih, assignors to Shell Oil Company, New York, 7

N.Y., a corporation of Delaware No Drawing. Filed Feb. 18, 1958, Ser. No. 715,858

10 Claims. (Cl. 184-1) This invention relates to the lubrication of high-speed bearings at high temperature. More particularly, it pertains to lubrication at temperatures of about 800 F. and higher as encountered in aircraft gas turbine engines and the'like,with a vaporous composition.

It has been proposed to use vaporous mixtures of air and light liquid hydrocarbons having an end boiling point of about 450 F. in certain proportions, preferably containing small amounts of reactive sulfur, chlorine and/or phosphorus-containing compounds as lubricants at temperatures as high as 700 F. However, it has been observed that above 700 F., especially at temperatures of about 800 F. or higher such as 1000 F. or above and at'speeds of 20,000 rpm. and above, vaporous air-hydrocarbon lubricant mixtures containing the mentioned loadcarrying agents are ineffective wear inhibitors. It has now been found'that superior lubrication can be provided for metal surfaces subjected to high speeds and temperatures of about 800 F. and higher, even to 1000 -F. and above, by contacting or blanketing the surfaces to be lubricated with a vaporous lubricant mixture comprising a substantial or major proportion of air and a minor am'ount of a vaporized polyoxyalky-lene fluid having a viscosity in its liquid state of not higher than 260 SUS at 100 F. The weight ratio of the two components should be from about 4:1 to about 13:1, preferably from about :1 to about :1, respectively. The mixture may contain, if desired, a minor amount of from about 0.01% to "about 5%, preferably from about 0.1% to 1% of a chemically reactive metal-free sulfurand/ or phosphoruscompound. a

Instead of air, other free-oxygen-containing gases can be used, such as other mixtures of free oxygen and nitrogen, as well as oxygen per se. In such a case, the ratio of the oxygen to hydrocarbon should be adjusted accordingly so that the ratio of free oxygen to hydrocarbon is equivalent to that of the free oxygen to the polyoxyalkylene fluid in the air-polyoxyalkylene fluid mixtures block copolymers of ethylene oxide and propylene oxide,

as Well as ether'and ester derivatives of said compounds of monohydric alcohols and phenols and of momentboxylic acids, in which the polyoxyalkylene constitutes themajor part of the product. The heteric copolyrners of ethylene oxide and 1,2-propylene oxide, as well as 2,952,335 Patented Sept. 13, 1969 their monoethers, having a viscosity range at 100 F. SUS of from about 50 to about 170 are preferred. By the term heteric copolymers is meant that the ethylene oxide and propylene oxide inratio of 75:25 to 10:90 and preferably in the ratio of 50:50 ethylene oxidezpropylene oxide is randomly polymerized as described in U.S. Patents 2,425,755 and 2,425,845. By block cOPolytners of ethylenev oxide and propylene oxide is meant that first one of the oxides, e.g., propylene oxide is polymerized and thereafterthis polymer is treated with a dissimilar alkylene oxide compound as described in U.S. Patent 2,677,700,

The ether and ester derivatives of these polymers are preferably alcohols and fatty acids of from 1 to about 10 oxide and 1,2-propylene oxide in the molar ratio of 50:50

as described in U.S. Patent 2,425,755 and having viscosities at 100 F. SUS of 55, 100 and 170 are preferred. Three illustrative ones of these :50 copolymers are characterized as follows: (A) viscosity, SUS at 100 F., pour point, F., 85; flash point, F., 260; fire point, F., 285; refractive index N 1.44; (B) pour point, flash point; F., 350; fire point, F., 430; refractive index N 1.450; (C) pour point, -45; flash point, F., 410; fire point, F., 475; refractive index N 1.453.

Still further improvement can be obtained by providing the metal bearing surfaces with a compound capable of coating or reacting with the metal and containing at least one element which exhibits acidic chemical properties, particularly the chemically acidic elements of groups V to VII of the periodic table. Those elements which are particularly eflective for this purpose are phosphorus, sulfur, selenium and tellurium, occurring in the right-hand side of groups V and VI. The surface compound can be provided in a separate and distinct operation, as by a pretreatment with a suitable active agent of the acidic element, and/ or in the same operation of lubrication as by incorporating the agent in the vaporous lubricating mixture.

The above surface active compounds appear to serve at least two functions, both advantageous to the effective lubrication. They provide a load carrying film, such as a metal phosphide or phosphate or a metal sulfide, and they are effective in minimizing the undesirable production of carbonaceous deposits, presumably in part by shielding the lubricating vaporous mixture at the elevated tempera:- ture from the catalytic activity of the metal of the bearing.

The surfaces to be lubricated may be chemically pretreated by various methods which are well known in the art.

Normally gaseous, liquid and solid chemically reactive agents are capable of forming protective films on the contacting metallic surfaces and they may be utilized' in the'gaseous, liquid or solid state. Materials which are readily utilized in the gaseous state include sulfur, hydro- .gen sulfide, .carbon disulfide, chlorine, etc. The sulfide or chloride film canbe formed on thesurface to be protectedby rsimply contacting jthegas with the hot metal surface to be protected. "In cases where reagents are used I 3 in the liquid state the metal surface can be dipped in, sprayed with, or painted with an aqueous or non-aqueous composition containing the reactive agent. Illustrative compositions are aqueous solutions of hydrogen sulfide, ammonium sulfide, ammonium polysulfide, sodium polyselenide, etc. The compositions can be a colloidal aqueous or oil suspension of sulfur, sulfurized oils, such as sulfurized lard oil, or mineral oil containing sulfur-ized lard oil and/or sulfur, dialkyl, diaryl or diarallyl sulfides or selenides, e.g., dilauryl sulfide, dibenzyl disulfide, dilauryl selenide, and the like. Phosphate films can be formed on the metal surface by treating the metal surface with an aqueous solution containing phosphoric acid or a phosphate salt, e.g., tri-sodium phosphate. The metal surface can also be dusted with a solid agent, such as sulfur flowers thereafter heated to form a sulfide film on the metal surface. Other methods of pretreating the surface to be lubricated include the heating of the metal in a mineral lubricating oil containing: (a) an organic phosphate or phosphite, such as an aryl or alkyl acid phosphate, e.g., diphenyl acid phosphorate, diethyl acid phosphorate, dilauryl acid phosphorate or an alkyl phos phite, such as triisopropyl phosphite or tributyl phosphite, and/or (b) a halogenated organic compound such as a chlorinated hydrocarbon, e.g., chlorinated olefin, fluorinated olefin, carbon tetrachloride, chlorinated naphthabearing break-in time, 4 hours, using white medicinal oil after which the oil was removed, the temperature increased to 1000 F. and the bearing lubricated with the compositions shown in Table I for 22 hours or until bearing failure occurred.

Standard bearing radial internal clearance measuring instrument used, made by Sheffield Corporation of Dayton, Ohio.

lene, chlorinated anthracene, chlorinated alkylbenzene,

chlorinated polar-containing compounds such as dichlorodibenzyl, disulfide and pentachlorophenol, tnichloroa-lkylphosphate, trifluoroacetic acid and mixtures thereof. Still other methods of forming anti-scufling, anti-seizing and wear resistant films on surfaces to be lubricated are described in Metal Coloring by Hiorns, Mcmillan Company of London. A preferred method of forming protective films is to run the assembled machine at a temperatnre of about 400 F. while lubricating with a lubricant containing the desired pretreating additive such as sulfurized mineral oil containing about 1% sulfur.

A preferred embodiment of the invention is to utilize from about 0.01% to about 1% of an extreme pressure and load carrying additive, more specifically, an organic phosphorus ester or an organic sulfide in the vaporous lubricant blend of air and a polyoxyalkylene fluid, e.g., copolymer A, described hereinbefore.

Phosphorus-containing compounds of this type include an organic phosphite or phosphate, such as the alkyl, cycloalkyl or aryl phosphite or phosphate, e.g., mono, di-, or tri-, methyl, ethyl, isopropyl, butyl, hexyl, octyl, cyclohexyl, phenyl phosphites, or phosphates, the preferred being the dior tri-(branched-chain alkyl) phosphites or phosphates such as tri-isopropyl phosphite or phosphate, and mixtures thereof. The organic sulfides include dialkyl, diaryl or diaral-lyl sulfides such as dilauryl disulfide, dibenzyl disulfide, etc. The phosphorus compound preferably contains only atoms of phosphorus, carbon, hydrogen and oxygen in the molecule.

The vaporous lubricant blend can be sprayed or atomized onto the surface to be lubricated such as gears and bearings so that the entire surface is enveloped or blanketed in a vaporous lubricant. Also, the lubricant may be vaporized into the air stream at any convenient location and the mixture conducted to the surface to be lubricated.

The lubricant mixture of air and polyoxyalkylene fluid can be used as a conventional lubricant during the periods of operation when machine parts are at temperatures below the end boiling point of the lubricant.

In order to demonstrate the effectiveness of vaporous lubricants of this invention at elevated temperatures and high speeds, a high-speed bearing assembly, as shown in Figure 2 of the Sorem et al. article High-Temperature Bearing Operation in Absence of Liquid Lubricants, July-- August 1956 issue of Lubrication Enginering, was lubricated with compositions shown in Table I below and the results are tabulated therein.

test conditions were: spindle rotation 20,000 r.p.m.;

b Cage and balls pitted and worn. Slight pitting and wear. d Cage and bearing in excellent condition.

Lubricants of this invention are particularly applicable for ball and roller bearings of gas turbine engines where operating temperatures are high and can also be used for lubrication of various other machines and equipment operating at high temperatures and speeds.

We claim as our invention:

1. A method of lubricatin metal surfaces subjected to a temperature of at least 800 F., which comprises contacting the surfaces with a vaporous lubricant consisting essentially of a blend of air and a polyoxyalkylene fluid having a viscosity at F. SUS of from 40 to about 260, in the weight ratio of from about 4:1 to about 13:1, respectively.

2. A process of lubricating metal surfaces subjected to a temperature of at least 800 E, which comprises contalcting the surfaces with a vaporous lubricant consisting essentially of a blend of air and a copolymer of ethylene oxide and propylene oxide having a viscosity at 100 F. of from about 40 to about 260, in the weight ratio of from about 5:1 to about 10: 1, respectively.

3. A method of lubricating metal surfaces subjected to a temperature of at least 800 R, which comprises contacting the surfaces with a vaporous lubricant consisting essentially of a blend of air and a heteric copolymer of ethylene oxide and 1,2-propylene oxide having a viscosity at 100 F. of from about 55 to about 170, in the Weight ratio of from about 5:1 to about 10:1, respectively.

4. A method of lubricating metal surfaces subjected to a temperature of at least 800 E, which comprises contacting the surfaces with a vaporus lubricant consisting essentially of a blend of air, a block copolymer of ethylene oxide and polypropylene oxide in the weight ratio of from about 5 :1 to about 10:1, respectively.

5. A method of lubricating metal surfaces subjected to a temperature of at least 800 R, which comprises contacting the surfaces with a vaporous lubricant consisting essentially of a blend of air and a polyoxyalkylene fluid having a viscosity at 100 F. SUS of from 40 to about 260, in the weight ratio of from 4:1 to about 13:1, respectively, said blend containing a minoramount of a reactive compound selected from the group consisting of an organic phosphite, a sulfide and mixtures thereof. i

6. A method of lubricating metal surfaces subjected to a temperature of at least 800 F., which comprises contacting the surfaces with a vaporous lubricant consisting essentially of a blend of air and a copolymer of ethylene oxide and propylene oxide having a viscosity at 100 F. of from about 40 to about 260, in the weight ratio of from about 5:1 to about 10: 1, respectively, said blend containing a minor amount of an alkyl phosphite. i 4

7. A method of lubricating metal surfaces subjected to a temperature of at least 800 R, which comprises contacting the surfaces with a vaporous lubricant consisting essentially of a blend of air and a heteric copolymer of ethylene oxide and 1,2-propylene oxide having a viscosity at 100 F. of from about 55 to about 170, in the weight ratio of from about 5:1 to about 10:1, respectively, said blend containing from about 0.01% to about 5% by weight by triisopropyl phosphite.

8. A method of lubricating metal surfaces subjected to a temperature of at least 800 R, which comprises contacting the surfaces with a vaporous lubricant consisting essentially of a blend of air and a heteric copolymer of ethylene oxide and 1,2-propylene oxide having a viscosity at 100 F. of from about 55 to about 170, in the weight ratio of from about 5:1 to about 10:1, respectively, said blend containing from about 0.01% to about 5% by weight of triisopropyl phosphite and dibenzyl disulfide.

9. A method of lubricating metal surfaces subjected to a temperature of at least 800 R, which comprises contacting the surfaces with a vaporous lubricant consisting essentially of a blend of air and a copolymer of ethylene oxide and propylene oxide having a viscosity at 100 F. of from about 40 to about 26 0, in the weight ratio of from about 5 :1 to about 10:1, respectively, said blend 'containing a minor amount of dibenzyl disulfide.

10. A method of lubricating metal surfaces subjected to a temperature of at least 800" R, which comprises contacting the surfaces with a vaporous lubricant consisting essentially of a blend of air and a copolymer of ethylene oxide and propylene oxide having a viscosity at 100 F. of from about 40 to about 2 60, in the weight ratio of from about 5:1 to about 10: 1, respectively, said blend containing a minor amount of carbon disulfide.

References Cited in the file of this patent UNITED STATES PATENTS 2,531,411 Davenport Nov. 28, 1950 2,764,866 Wasserbach et a1. Dot. 2, 1956 2,839,468 Stewart et al.. June 17, 1958 FOREIGN PATENTS 680,619 Great Britain Oct. 8, 1952 OTHER REFERENCES Gas Turbine Fuels and Lubricants, Aero Digest, vol. 57, No. 1, July 1948, page 95. 

